All is not lost: Post-saccadic contributions to the perceptual omission of intra-saccadic streaks

Moving fast and seeing slow? The visual consequences of vigorous movement

In active agents, sensory and motor processes form an inevitable bond. This wedding is particularly striking for saccadic eye movements - the prime target of Shadmehr and Ahmed's thesis - which impose frequent changes on the retinal image. Changes in movement vigor (latency and speed), therefore, will need to be accompanied by changes in visual and attentional processes. We argue that the mechanisms that control movement vigor may also enable vision to attune to changes in movement kinematics.

Intrasaccadic motion streaks jump-start gaze correction

Rapid eye movements (saccades) incessantly shift objects across the retina. To establish object correspondence, the visual system is thought to match surface features of objects across saccades. Here, we show that an object's intrasaccadic retinal trace-a signal previously considered unavailable to visual processing-facilitates this match making. Human observers made saccades to a cued target in a circular stimulus array. Using high-speed visual projection, we swiftly rotated this array during the eyes' flight, displaying continuous intrasaccadic target motion. Observers' saccades landed between the target and a distractor, prompting secondary saccades. Independently of the availability of object features, which we controlled tightly, target motion increased the rate and reduced the latency of gaze-correcting saccades to the initial presaccadic target, in particular when the target's stimulus features incidentally gave rise to efficient motion streaks. These results suggest that intrasaccadic visual information informs the establishment of object correspondence and jump-starts gaze correction.

Saccadic suppression in schizophrenia

About 40% of schizophrenia patients report discrete visual disturbances which could occur if saccadic suppression, the decrease of visual sensitivity around saccade onset, is impaired. Two mechanisms contribute to saccadic suppression: efference copy processing and backwards masking. Both are reportedly altered in schizophrenia. However, saccadic suppression has not been investigated in schizophrenia. 17 schizophrenia patients and 18 healthy controls performed a saccadic suppression task using a Gabor stimulus with individually adjusted contrast, which was presented within an interval 300 ms around saccade onset. Visual disturbance scores were higher in patients than controls, but saccadic suppression strength and time course were similar in both groups with lower saccadic suppression rates being similarly related to smaller saccade amplitudes. Saccade amplitudes in the saccadic suppression task were reduced in patients, in contrast to unaltered amplitudes during a saccade control task. Notably, smaller saccade amplitudes were related to higher visual disturbances scores in patients. Saccadic suppression performance was unrelated to symptom expression and antipsychotic medication. Unaltered saccadic suppression in patients suggests sufficiently intact efference copy processing and backward masking as required for this task. Instead, visual disturbances in patients may be related to restricted saccadic amplitudes arising from cognitive load while completing a task.

Intra-saccadic motion streaks as cues to linking object locations across saccades

When visual objects shift rapidly across the retina, they produce motion blur. Intra-saccadic visual signals, caused incessantly by our own saccades, are thought to be eliminated at early stages of visual processing. Here we investigate whether they are still available to the visual system and could—in principle—be used as cues for localizing objects as they change locations on the retina. Using a high-speed projection system, we developed a trans-saccadic identification task in which brief but continuous intra-saccadic object motion was key to successful performance. Observers made a saccade to a target stimulus that moved rapidly either up or down, strictly during the eye movement. Just as the target reached its final position, an identical distractor stimulus appeared on the opposite side, resulting in a display of two identical stimuli upon saccade landing. Observers had to identify the original target using the only available clue: the target's intra-saccadic movement. In an additional replay condition, we presented the observers’ own intra-saccadic retinal stimulus trajectories during fixation. Compared to the replay condition, task performance was impaired during saccades but recovered fully when a post-saccadic blank was introduced. Reverse regression analyses and confirmatory experiments showed that performance increased markedly when targets had long movement durations, low spatial frequencies, and orientations parallel to their retinal trajectory—features that promote intra-saccadic motion streaks. Although the potential functional role of intra-saccadic visual signals is still unclear, our results suggest that they could provide cues to tracking objects that rapidly change locations across saccades.

An adaptive algorithm for fast and reliable online saccade detection

To investigate visual perception around the time of eye movements, vision scientists manipulate stimuli contingent upon the onset of a saccade. For these experimental paradigms, timing is especially crucial, because saccade offset imposes a deadline on the display change. Although efficient online saccade detection can greatly improve timing, most algorithms rely on spatial-boundary techniques or absolute-velocity thresholds, which both suffer from weaknesses: late detections and false alarms, respectively. We propose an adaptive, velocity-based algorithm for online saccade detection that surpasses both standard techniques in speed and accuracy and allows the user to freely define the detection criteria. Inspired by the Engbert-Kliegl algorithm for microsaccade detection, our algorithm computes two-dimensional velocity thresholds from variance in the preceding fixation samples, while compensating for noisy or missing data samples. An optional direction criterion limits detection to the instructed saccade direction, further increasing robustness. We validated the algorithm by simulating its performance on a large saccade dataset and found that high detection accuracy (false-alarm rates of < 1%) could be achieved with detection latencies of only 3 ms. High accuracy was maintained even under simulated high-noise conditions. To demonstrate that purely intrasaccadic presentations are technically feasible, we devised an experimental test in which a Gabor patch drifted at saccadic peak velocities. Whereas this stimulus was invisible when presented during fixation, observers reliably detected it during saccades. Photodiode measurements verified that-including all system delays-the stimuli were physically displayed on average 20 ms after saccade onset. Thus, the proposed algorithm provides a valuable tool for gaze-contingent paradigms.

Retinal image quality in near-eye pupil-steered systems

State-of-the-art near-eye displays often compromise on eye box size to maintain a wide field of view, necessitating a means for steering the eye box to maintain alignment with a moving eye. The design space of such pupil-steered systems is not well defined and the implications of imperfect steering on the perceived image are not well understood. To better characterize the pupil steering design space, we introduce a generalized taxonomy of pupil-steered architectures that considers both system and ocular factors that affect steering performance. We also develop an optical model of a generalized pupil-steered system with a wide-field schematic eye to simulate the retinal image. Using this framework, we systematically characterize retinal image quality for different combinations of design parameters. The results of these simulations provide an overview of the pupil steering design space and help determine relevant psychophysical experiments for further evaluation.

The Joy of Retinal Painting: A Build-It-Yourself Device for Intrasaccadic Presentations

As the eyes move, they incessantly impose motion blur on the retinal image, yet our perception of the world remains undisturbed. In fact, it is often assumed that intrasaccadic visual signals are largely eliminated from processing by a dedicated suppression mechanism. Here, we describe an easy-to-build presentation device that produces a stimulus that is highly salient and well resolvable during saccades: Using LED strips with high temporal resolution, any type of text and image stimulus can be presented in an anorthoscopic fashion—as if seen through and travelling behind a narrow slit—at very short durations. Whereas these stimuli appear as a brief flash during fixation, saccades spread them across the retina, producing spatially extended and well-resolved retinal images. In fact, retinally painted images induced by saccades across a series of anorthoscopic image presentations were correctly identified by observers in 90% of all cases. So why should we suppress intrasaccadic perception if it enables us to experience the joy of retinal painting?

Reinforcement reduces the size-latency phenomenon: A cost-benefit evaluation of saccade triggering

Saccadic latencies are known to change as a function of target eccentricity and size. Recently, it has been shown that latencies consistently change according to the amplitude of the step in proportion to the size of the target (Madelain, Krauzlis, & Wallman, 2005; Harwood, Madelain, Krauzlis, & Wallman, 2008; De Vries, Azadi, & Harwood, 2016). This effect, called the size-latency phenomenon, might be seen as a function of a cost-benefit relationship: Longer latencies might be explained by the lower benefit of making a saccade while the target mostly remains within the attentional field. Here, we probe this hypothesis by manipulating the cost-benefit relationship using a reinforcement procedure. Participants tracked a target stepping horizontally with varying amplitudes and sizes such that the step-to-size ratio was equal to either 0.3 or 1.5. We used a dynamic-reinforcement criterion in the blocked conditions. In the 0.3-ratio condition, any latency shorter than the criterion was reinforced. In the 1.5-ratio condition, any latency longer than the criterion was reinforced. During baseline, we observed the size-latency effect with large differences in latencies depending on the ratio in force (229 and 161 ms, respectively, for 0.3 and 1.5). After learning, distributions shifted toward the shorter or longer value (198 and 236 ms, respectively, for 0.3 and 1.5). On average, latencies decreased by 31 ms and increased by 75 ms according to the ongoing reinforcement contingencies. Our results indicate that reinforcement contingencies can considerably affect saccadic-latency distributions, and support the idea of a cost-benefit evaluation of saccade triggering.